With the development and availability of different data formats for multimedia content, it is often desirable to have contents in different data formats on a single data disc. To manufacture these hybrid discs, it is necessary to modify conventional fabrication processes and/or systems typically used for single format discs.
To facilitate understanding of the embodiments of the present principles, some background relating to a conventional optical disc and its manufacturing process is provided in FIG. 1 and FIG. 2a-d, respectively.
FIG. 1 is a schematic illustration of a conventional dual layer optical disc. The optical disc 100 has a substrate 102, a first reflective layer 104, a spacer or bonding layer 106, a second reflective layer 108, and a layer 110. For a Blu-ray disc (BD), layer 110 is a cover layer, and for a digital versatile disc (DVD), layer 110 is a second substrate. For a BD, the substrate 102 is typically a 1.1 mm polycarbonate disc, and the first reflective layer 104, which is highly or substantially totally reflective at the read-out wavelength, can be made of a silver alloy or aluminum with a thickness of less than about 50 nm. The second reflective layer 108, which is partially reflective, can be made of a silver alloy with a thickness of less than about 20 nm. The Blu-ray spacer layer 106 is made of a transparent resin material and has a thickness of about 25 μm, and the cover layer is made of a transparent material with a thickness of about 75 μm, and may also include a protective hard coating.
Presently, there are two widely used methods for manufacturing dual-layer Blu-ray optical discs. One is a plastic stamper method, and the other is a “wet embossing” method. The plastic stamper method is also referred to as a “2P” process, which stands for photo polymerization (referring to one of the steps in the method). The method involves molding a first data layer in a first substrate, and a second data layer in a second substrate. After a reflective layer is formed over the first data layer, the two substrates are bonded to each other using an adhesive. The second substrate is then separated and discarded, leaving an impression of the second data layer molded into the adhesive layer remaining on the first substrate. Additional processing steps are performed to complete the fabrication of the disc. In the case of Blu-ray discs, the first substrate is a 1.1 mm disc, and the second substrate may be a 0.6 mm disc.
The 2P method is further illustrated with reference to FIGS. 2a-d, which depict cross-sectional views showing various stages during the fabrication of an optical disc, e.g., a Blu-ray disc. FIG. 2a shows a first substrate 202, e.g., a 1.1 mm thick polycarbonate disc, with a surface 202D having structures such as pits and lands representing data in a first data layer. A first reflective layer 204 is formed over the molded surface 202D of the substrate 202. A different substrate 250, e.g., a polycarbonate disc, typically with a thickness of 0.6 mm, has a surface 250D with pits and lands representing data in a second data layer. Surfaces 202D and 250D are molded using respective stampers (not shown).
The substrate 250 is bonded to the reflective layer 204 with an adhesive layer 206 (which may be made of two separate layers of different adhesive materials), as shown in FIG. 2b. After curing the adhesive by exposure to ultra-violet (UV) light (through photo polymerization of the adhesive), the substrate 250 is mechanically stripped from the reflective layer 204, leaving the data layer impression on a surface 206D of the adhesive layer 206, as shown in FIG. 2c. Since the substrate 250 is discarded after this fabrication, and effectively serves as a stamper for transferring the data layer onto the adhesive 206, it is also referred to as a sacrificial plastic stamper.
The substrate structure in FIG. 2c has two data layers—one molded on the substrate 202 and the other on adhesive layer 206. A reflective layer 208 is then formed over the data surface 206D of the adhesive layer 206, e.g., by sputtering, and a cover layer 210 is applied over the reflective layer 208, resulting in an optical disc 200, as shown in FIG. 2d. 
Another conventional method for making discs is the “wet embossing” method, which starts by molding the first data layer in the 1.1 mm Blu-ray disc polycarbonate substrate 202 as shown in FIG. 2a. After applying the first reflective layer 204, one or two layers of lacquer (not shown), including a wet embossing lacquer, are applied over the reflective layer 204. The second data layer is embossed in the wet lacquer using a re-usable nickel stamper and the lacquer is UV-cured on the stamper. The disc structure is subsequently removed from the stamper, and fabrication is completed by performing additional steps such as those described above in connection with FIG. 2c-d. 
Typically in disc manufacture, individual substrates are stacked on spindles of about 100 to 150 discs for transport between sequential manufacturing processes (e.g. replication, printing, and packaging). To facilitate the ease of un-stacking, molded spacers or “stacking rings” are provided on the underside of substrates. In the case of certain intermediate replication processes, the molded stacking rings fail to provide sufficient clearance to allow un-stacking or disc separation by typical automated handling methods. The flat or smooth adjacent disc surfaces on spindles of 100-150 discs used to transport substrates cause the substrates to stick together such that downstream automation processes are negatively impacted.